1. Technical Field
A method for fabricating semiconductor devices is disclosed which includes forming contacts using ArF lithography technology.
2. Description of the Related Art
As the integration of a semiconductor device increases, it is difficult to effectively secure a desired active open area by using a direct contact method because the alignment margin of lithography processes is reduced. To alleviate the above problem, a self alignment contact (SAC) process has been introduced using a different etching ratio of a dual insulating layer including an oxide layer and a nitride layer.
A process for fabricating a semiconductor device has been developed using lithography technology. Many believe that the future of the integration of semiconductors will depend on resolution improvement of current photolithography technology.
Generally, lithography processes are carried out with an exposing process and a developing process. Recently, lithography processes usually represent an exposing process and lithography technology is classified into optical lithography or non-optical lithography. Lithography technology is employed to form a circuit substrate of various materials on a substrate.
After a photoresist (PR), polymer is coated on a substrate, the substrate is exposed through a mask (or reticle) and photosensitivity is caused in the areas in which the PR is exposed to light. Subsequently, a developing process follows and a photoresist pattern is formed. Finally, a desired pattern can be obtained by using the photoresist pattern as a barrier in an etching process.
Since the mass-production of semiconductor devices based on DRAM began, lithography technology has been rapidly developed. Integration of the DRAM has been increased four times in a three-year period. Other memory devices followed the DRAM in two to three years. The design of the semiconductor memory device developed from 0.8 xcexcm of 4 MB DRAM to 0.13 xcexcm of 4 GB DRAM as non-optical lithography technology was introduced.
The resolution of a lithography process is in inverse proportion to a wavelength of a light source. A wavelength of a light source used in a xe2x80x9cstep and repeat projection systemxe2x80x9d is from 436 nm (g-line) to 365 nm (i-line). Recently, exposure equipment of a stepper or scanner type using DUV (deep ultra violet) of a wavelength of 248 nm, which is a wavelength of a KrF excimer laser, is commonly used.
The lithography technology has been developed not only with exposure equipment, such as a high numerical aperture lens of over 0.6 mm and hardware that provide apertures and alignment, but also with at a resist material, such as a resist of a chemically amplified resist type or the like. Also, tri-linear resist (TLR), bi-linear resist (BLR), top surface imaging (TSI), anti reflective coating (ARC) processes have been developed as well as phase shift mask (PSM) and optical proximity correction technologies.
Since DUV lithography technology of a wavelength of 248 nm has problems of a time delay and a base material dependency, it has been used in products of 0.18 xcexcm design. However, in order to develop products of below 0.15 xcexcm design, a new DUV lithography technology having a wavelength of 193 nm (ArF excimer laser) has to be developed. Even if several technologies are employed in the new DUV lithography technology to increase resolution, it is impossible to form patterns of below 0.1 xcexcm so that a new lithography technology having a new light source has been developed. Recently, the most approached technology is an exposure equipment using a electron beam and a X-ray as a light source. In addition, an EUV (extreme ultraviolet) technology using a weak X-ray as a light source has been developed. It is still impossible to estimate which the lithography technology will be adopted as the next generation photolithography technology. It will most likely be determined within two or three years.
The initial exposure equipment is a contact printer, where a mask is directly contacted with a substrate and aligned by an operator who looks directly at the mask and the substrate with the naked eye. As the gap between the substrate and the mask is decreased, resolution can be improved and the substrate is exposed with an approach printer, such as soft contact or hard contact (below 10 xcexcm) depending on the gap.
In the early 1970s, exposure equipment of a projection type applying an optical device using reflection or refraction of light was developed, resolution was improved and the lifetime of a mask was extended. As a result, the exposure equipment of the projection type started to be applied into the product development of large substrates.
In the mid-1970s, use of a stepper using a projection optical device began, started the development of lithography technology which contributed to mass-production of semiconductors. The stepper is an abbreviated form of xe2x80x9cstep and repeat.xe2x80x9d The exposure equipment using the stepper was implemented to improve the resolution and alignment accuracy. In the initial stepper, a reduced projection exposing method, which a ratio of the mask pattern to the substrate was 5:1 or 10:1, was designed. However, the reduced projection exposing method of 5:1 was generally employed due to limitations of the mask pattern.
A scanner of a xe2x80x9cstep and scanningxe2x80x9d type was developed in the early 1990s, which reduced the ratio to 4:1. However, the scanner performed poorly in terms of the mask pattern, whereas the scanner as an exposure equipment was used to increase production efficiency and was applied more regularly as chip sizes decreased.
The resolution is largely related with wavelength of the light source. An initial exposure equipment using g-line (wavelength (xcex)=436 nm) could implement a pattern of a 0.5 xcexcm level and exposure equipment using i-line (xcex=365 nm) could implement a pattern of a 0.3 xcexcm level. Recently, an exposure equipment using a KrF laser (xcex=248 nm) and a new resister have developed and additional processes have improved. As a result, it is possible to form a pattern of below 0.15 xcexcm.
Now, an exposure equipment using an ArF laser (xcex=193 nm) is developed to form a pattern of 0.11 xcexcm. The DUV lithography technology has excellent resolution for the i-line and DOF, however, such technology is difficult to control. This problem can arise optically due to a short wavelength and/or a chemically due to use of a chemical amplified resister. When the wavelength becomes shorter, critical dimension (CD) variation due to a standing wave and overdeveloping by reflection light due to a difference of base phases results. The CD variation of a line width is periodically changed by interference of incident light and reflective light and is changed by a minute difference of a width of a resister or a difference of a width of a base film. A chemical amplified resist has to be employed for improving sensitivity in the DUV process. However, there are problems of PED (post exposure delay) stability, base dependency and the like with respect to the reaction mechanism.
ArF exposure technology was introduced after the KrF exposure technology. A main issue with ArF exposure technology is the development of a resister for ArF. Basically, the resister used for KrF has to be improved to be used for ArF. However, a resister with a benzene ring structure cannot be used as the ArF resister. The resister with the benzene ring structure is used as the KrF resister for the i-line to secure tolerance for dry etching. When the resister with the benzene ring structure is used as the ArF resister, since absorbency is increased in a wavelength of 193 nm, which is a wavelength of the ArF laser, light permeability is reduced so that it is impossible to expose the lower side of the resister. Accordingly, a resister, which does not have a benzene structure, secures tolerance for dry etching, has good adhesion and can be developed with 2.23% TMAH, has been developed. The ArF resisters are reported in the literature.
Resisters of a polymer type of a COMA (cycloolefin-maleic anhydride) family or an acrylate family and resisters of a mixture type, which are commercially used, have a benzene ring structure.
When the ArF lithography technology is employed, pattern transformation of a striation type in a landing plug contact (LPC) process is caused or a PR cluster or plastic deformation is cause in the SAC etching process. Also, the PR can be clustered on one side in the SAC etching process.
FIGS. 1A to 1B are the cross-sectional views showing a process for forming contact with the ArF lithography technology according to the prior art.
Referring to FIG. 1A, a layer 11 to be etched is formed on a semiconductor substrate 10 and an organic anti-reflective layer 12 is coated on the layer 11 for preventing scattered reflection in exposing process. After a photo resistor is coated on the anti-reflective layer 12, a photoresist pattern 13 is formed by using the ArF lithography technology.
The layer 11 may include an insulating layer such as BPSG (boro phospho silicate), SOG (spin on glass), field oxide layer using an oxide or a nitride layer, interlayer insulating layers and hard mask layer. In addition, the layer 11 can further include a bitline using metal, such as polysilicon, tungsten or the like, and wordline which are formed with photoresist pattern 13.
Referring to FIG. 1B, as the anti-reflective layer 12 and the layer 11 are etched by using the photoresist pattern 13 as a mask, the contact hole 14 is formed. The photoresist pattern 13 and the anti-reflective layer 12 are removed.
The anti-reflective layer 12 is etched by using an etching gas including a fluorine gas, such as a CxFy (where, x is 1 to 5 and y is 1 to 10), CxHyFz (where, x, y and z are 1 to 3), SxFy (where, x is 1 to 5 and y is 1 to 10) or the like, or a mixture gas of a metal etching gas, such as a Cl2, BCl3 or HBR gas, and an O2 gas. When the layer 11 is one of insulating layers, the layer 11 is etched by using an etching gas including a fluorine gas, such as a CxFy (where, x is 1 to 5 and y is 1 to 10), CxHyFz (where, x, y and z are 1 to 3), SxFy (where, x is 1 to 5 and y is 1 to 10) or the like. When the layer 11 is a metal layer, the etched layer is etched by a metal etching gas, such as a Cl2, BCl3 or HBR gas.
The photoresist pattern 13 is transformed such as xe2x80x98Axe2x80x99 in FIG. 1B by an etching gas, temperature, pressure, time, or the like so that an etching shape of the etched layer 11 is transformed.
A method for forming a self alignment contact (SAC) with an ArF lithography technology using a low-k dielectric layer to prevent PR pattern transformation and loss is disclosed.
A method for forming a contact in a semiconductor device is disclosed that comprises: a) forming a layer to be etched on the semiconductor substrate; b) successively forming a low-k dielectric sacrifice layer and a hard mask on the etched layer; c) forming an anti-reflective layer and a photoresist pattern on the hard mask by using ArF lithography technology; d) selectively etching the anti-reflective layer and the hard mask and simultaneously removing the photoresist pattern when etching the hard mask; e) forming a contact hole exposing a surface of the semiconductor substrate by etching the low-k dielectric sacrifice layer and the layer by using the hard mask as a mask; and f) removing the hard mask and the low-k dielectric sacrifice layer.